Apoptosis signal-regulating kinase 1 (ASK-1) is a member of the mitogen-activated protein kinase kinase kinase (MAPKKK, MAP3K) family, which when activated phosphorylates downstream MAP kinase kinases (MAPKK, MAP2K), which in turn activate MAP kinases (MAPK). MAPKs elicit a response by phosphorylating cellular substrates, thus regulating the activity of transcription factors that ultimately control gene expression. Specifically ASK-1, also known as MAPKKK5, phosphorylates MAPKK4/MAPKK7 or MAPKK3/MAPKK6, which subsequently phosphorylates and activates the c-Jun N-terminal protein kinase (NK) and p38 MAPKs, respectively (H. Ichijo, et al., Cell Comm. Signal 2009, 7, 1-10; K. Takeda, et al., Annu. Rev. Pharmacol. Toxicol. 2008, 48, 199-225; H. Nagai, et al., J. Biochem. Mol. Biol. 2007, 40, 1-6). Activation of the JNK and p38 pathways triggers a downstream stress response such as apoptosis, inflammation, or differentiation (H. Ichijo, et al., Science 1997, 275, 90-94; K. Takeda, et al., J. Biol. Chem. 2000, 275, 9805-9813; K. Tobiume, et al., EMBO Rep. 2001, 2, 222-228; K. Sayama et al., J. Biol. Chem. 2001, 276, 999-1004).
The activity of ASK-1 is regulated by thioredoxin (Trx), which binds to the N-terminal end of ASK-1 (M. Saitoh, et al., EMBO J. 1998, 17, 2596-2606). ASK-1 is activated succeeding autophosphorylation at Thr838 in response to environmental stimuli including oxidative stress, lipopolysaccharides (LPS), reactive oxygen species (ROS), endoplasmic reticulum (ER) stress, an increase in cellular calcium ion concentrations, Fas ligand, and various cytokines such as tumor necrosis factor (TNF) (H. Nishitoh, et al., Genes Dev. 2002, 16, 1345-1355; K. Takeda, et al., EMBO Rep. 2004, 5, 161-166; A. Matsuzawa, et al., Nat. Immunol. 2005, 6, 587-592).
ASK-1 has been associated with autoimmune disorders, neurodegenerative disorders, inflammatory diseases, chronic kidney disease, cardiovascular disease, metabolic disorders, and acute and chronic liver diseases (R. Hayakawa, et al., Proc. Jpn. Acad., Ser. B 2012, 88, 434-453).
More specifically, ASK-1 has been associated with hepatic steatosis, including non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH). In a mouse model, high fat diets have caused induction of hepatic steatosis, ultimately causing fat accumulation and fatty acid oxidation. This led to the generation of ROS which caused hepatocyte dysfunction and death (S. K. Mantena, et al., Free Radic. Biol. Med. 2008, 44, 1259-1272; S. K. Mantena, et al., Biochem. J. 2009, 417, 183-193). Moreover, TNF was shown to be critical for apoptosis of hepatocytes through the ASK-1-JNK pathway, and TNF deficient mice showed reduced hepatic steatosis and fibrosis (W. Zhang, et al., Biochem. Biophys. Res. Commun. 2010, 391, 1731-1736).
Small molecule compounds which act as ASK-1 inhibitors have been disclosed in the following publications: WO 2008/016131, WO 2009/027283, WO 2009/0318425, WO 2009/123986, US 2009/0318425, WO 2011/041293, WO 2011/097079, US 2011/0009410, G. P. Volynets, et al., J. Med. Chem. 2011, 54, 2680-2686, WO 2012/003387, WO 2012/011548, WO 2012/080735, Y. Terao, et al., Bioorg. Med. Chem. Lett. 2012, 22, 7326-7329, WO 2013/112741, G. P. Volynets, et al., Eur. J. Med. Chem. 2013, 16, 104-115, US 2014/0018370, WO 2014/100541, WO 2015/095059, WO 2016/049069, WO 2016/049070, WO 2018/090869, WO 2018/133865, WO 2018/133866, WO 2018/148204, WO 2018/149284, WO 2018/151830, WO/2018/157856, WO 2018/157857, WO 2018/160406, WO 2018/169742, WO 2018/183122, WO 2018/187506, WO 2018/209354, WO 2018/218042, WO 2018/218044, WO 2018/218051, WO 2018/233553, US 2019/0062310, WO 2019/070742, WO 2019/050794, WO 2019/051265, and WO 2019/034096.
There is a need for the development of ASK-1 inhibitors for the treatment and prevention of disease.